Imaging system, imaging apparatus, lens unit, and method of controlling imaging system

ABSTRACT

An imaging system has an interchangeable lens and a camera body capable of communicating with the interchangeable lens. A camera control unit of the camera body acquires focus-sensitivity-related information (including sensitivity information at an image height of the center and correction information of the sensitivity that changes depending on the image height) from a lens control unit of the interchangeable lens through communication at a suitable timing. The camera control unit corrects a change of the sensitivity caused by the image height using image height information of a focus detection region selected from a plurality of focus detection regions and the acquired focus sensitivity correction information. The camera control unit calculates a driving amount of the focus lens from the focus detection signal using the corrected focus sensitivity, generates a control signal for instructing the driving amount, and transmits the control signal to a lens control unit.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an auto-focus (AF) control technologyin an imaging system having a lens unit that can be installed in acamera body.

Description of the Related Art

In order to drive a focus lens in an imaging apparatus, a driving amountof the lens is determined based on focus sensitivity. The focussensitivity is a coefficient for converting a defocus amount detected bythe imaging apparatus into a driving amount of the focus lens. In aninterchangeable lens type camera system, the focus sensitivity isdetermined based on optical information of the interchangeable lens.

In Japanese Patent Laid-Open No. S59-151116, a camera system in whichthe focus sensitivity is variable depending on focal length informationof the lens is disclosed. Using the camera system discussed in JapanesePatent Laid-Open No. S59-151116, it is possible to appropriately set thefocus sensitivity depending on the focal length and reduce a focusingtime. In addition, in Japanese Patent Laid-Open No. 2014-29353, a methodof determining defocus correction data based on a camera state such as aspatial frequency is disclosed.

Here, practical focus sensitivity is changed depending on a focusdetection position (image height) as well as focal length information ofthe lens. The technique of the related art disclosed in Japanese PatentLaid-Open No. S59-151116 fails to consider a change of the focussensitivity depending on the image height. For this reason, it isdifficult to set the focus sensitivity suitable for focusing of thesurrounding image height and perform accurate focus control in the eventof hunting or the like. In order to acquire more accurate focussensitivity, it is necessary to acquire focus sensitivity for everyimage height.

On the other hand, the focus sensitivity information is received incommunication through a mount terminal between the camera body and theinterchangeable lens. The technique of the related art disclosed inJapanese Patent Laid-Open No. 2014-29353 fails to consider a change ofthe data in communication depending on the image height. If differentdata is transmitted for each image height, a communication data amountincreases as the focus correction accuracy at the surrounding imageheight increases. In this case, it is necessary to transmit or receivenecessary data within a limited communication band between the camerabody and the interchangeable lens.

SUMMARY OF THE INVENTION

The present invention is to improve focus correction accuracy byacquiring sensitivity information and sensitivity correction informationin communication between the lens unit and the camera body.

According to an aspect of the present invention, an imaging system isprovided that includes a lens unit; and a camera body in which the lensunit is capable of being installed, wherein the lens unit comprises: afocus adjustment lens; a driving control unit configured to controldriving of the focus adjustment lens; and a first communication unitconfigured to communicate with the camera body, wherein the camera bodycomprises: a second communication unit configured to communicate withthe lens unit; a detection unit configured to acquire a focus detectionsignal in a plurality of regions; and a control unit configured togenerate a control signal for controlling driving of the lens using thefocus detection signal and transmit the control signal to the lens unitthrough the second communication unit, wherein the control unit of thecamera body acquires, through the second communication unit from thelens unit, conversion information for converting a focus detectionsignal to a driving amount of the lens and correction information of theconversion information indicating a change of the conversion informationcorresponding to an image height, wherein the control unit selects aregion used to control the driving of the lens from the plurality of theregions after acquiring the conversion information and the correctioninformation, and wherein the control unit generates the driving amountof the lens as the control signal from the conversion information andthe correction information in association with the image height of theselected region.

According to the present invention, it is possible to improve focuscorrection accuracy by acquiring sensitivity information and sensitivitycorrection information in communication between the lens unit and thecamera body.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an imaging system according to anembodiment of the present invention.

FIGS. 2A and 2B are schematic diagrams illustrating a configuration ofan imaging element according to an embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating a pixel portion of theimaging element according to an embodiment of the present invention.

FIG. 4 is a conceptual diagram illustrating a bundle of light beams thatemerge from an exit pupil of a photographic lens and are incident on theimaging element.

FIG. 5 is an explanatory diagram illustrating a multi-point auto-focus(AF) frame according to an embodiment of the present invention.

FIG. 6 is a diagram illustrating a process of selecting a multi-point AFframe according to an embodiment of the present invention.

FIG. 7 is a timing chart illustrating timing control for the multi-pointAF frame according to an embodiment of the present invention.

FIG. 8 is a flowchart illustrating a process of selecting an AF frame inthe multi-point AF operation and correcting sensitivity according to afirst embodiment of the present invention.

FIG. 9 is a flowchart illustrating a process of selecting an AF frame inthe multi-point AF operation and correcting sensitivity according to asecond embodiment of the present invention.

FIG. 10 is a graph illustrating a sensitivity ratio and a sensitivitycorrection ratio according to the second embodiment of the presentinvention.

FIG. 11 is a diagram illustrating a process of setting a sensitivitycorrection execution range according to the second embodiment of thepresent invention.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, each embodiment will be described with reference toaccompanying drawings. A configuration and an operation of an imagingdevice to which an imaging processing apparatus is applied that arecommon to each embodiment will be described first and then eachembodiment will be described. In each embodiment, a camera with a lensdevice mounted on an imaging device main body is described as anexample, but the present invention is applicable to an informationprocessing apparatus or the like having a camera or an imaging unit inwhich a lens and an imaging device main body are integrally configured.

First Embodiment

FIG. 1 is a block diagram illustrating an exemplary configuration of aninterchangeable camera-lens system having a camera body 1 and aninterchangeable lens 2 according to a first embodiment of the invention.The camera body 1 is allowed to communicate with the detachablyinstalled interchangeable lens 2. An electric circuit module 3 of thecamera body 1 has an imaging element 4 by which a subject image formedby light passing through the interchangeable lens 2 is photoelectricallyconverted into an electric signal. The imaging element 4 is acharge-coupled device (CCD) sensor, a complementary metal-oxidesemiconductor (CMOS) sensor, or the like and has a plurality of focusdetection pixels having different image heights.

The photometric unit 5 measures the amount of light (luminance) passingthrough the interchangeable lens 2 based on an output from the imagingelement 4 and outputs a result of the measurement. A focus detectionunit 6 calculates a defocus amount of the interchangeable lens 2 basedon each output of the plurality of focus detection pixels of the imagingelement 4 having different image heights. A period of the focusdetection process is synchronized with a frame rate corresponding to aphotographing duration (hereinafter referred to as a “VD”). Acommunication process between the camera body 1 and the interchangeablelens 2 is performed in synchronization with a VD signal.

A shutter control unit 7 controls a shutter opening/closing operation(not shown) for controlling an exposure amount of the imaging element 4.An image processing unit 8 performs various processes for the outputfrom a predetermined number of imaging pixels provided in the imagingelement 4 to create image data. The various processes include processesusing stored information of the interchangeable lens 2 and the storedinformation of the camera body 1.

A camera control unit 9 serves as a control center of the imagingapparatus provided with a central processing unit (CPU), a memory, andthe like. The camera control unit 9 controls operations of eachcomponent of the imaging apparatus. The camera body 1 is provided with acamera communication unit 11, and the interchangeable lens 2 is providedwith a lens communication unit 25, so that the camera control unit 9 cancommunicate with the lens control unit 26 through such communicationunits. The camera control unit 9 calculates an f-number or a shutterspeed in photographing based on the luminance acquired from thephotometric unit 5 and transmits a diaphragm driving command includingthe f-number to the lens control unit 26. Further, the camera controlunit 9 calculates a driving direction and a driving amount of the focuslens 22 of the interchangeable lens 2 to an in-focus position based onthe focus detection information and the information acquired from thelens control unit 26. The focus detection information includes thedefocus amount calculated by the focus detection unit 6. The informationacquired from the lens control unit 26 includes focus sensitivityinformation in the image height of the center and information on animage height change coefficient of the focus sensitivity. The cameracontrol unit 9 transmits, to the lens control unit 26, a control signalof the focus driving command for instructing the calculated drivingdirection and amount and performs focus control of the imaging opticalsystem. An auto-focus (AF) process of the camera body 1 side is aprocess of calculating the defocus amount in the focus detectionoperation and transmitting the control signal of the focus drivingcommand from the camera control unit 9 to the lens control unit 26. Animage plane AF operation to be described below is performed in everysingle vertical period 1V at the timing of the frame rate of the imagecapturing. For this reason, communication of information such as thefocus sensitivity, the focus position, and the driving state is executedin every single vertical period 1V. The vertical period “1V” correspondsto a period of a vertical synchronizing signal.

A lens installation detector 10 has a switch, a photodetector, or thelike to detect whether or not the interchangeable lens 2 is installed inthe camera body 1. The lens installation detector 10 outputs a detectionsignal to the camera control unit 9. The camera communication unit 11 ispaired with the lens communication unit 25, so that the camera controlunit 9 acquires various types of information stored in the lens controlunit 26. The various types of information include, for example, focussensitivity information and sensitivity correction information. Thesensitivity correction information is a sensitivity image heightcorrection coefficient for correcting the focus sensitivity that changesdepending on the image height. In the following description, suchinformation will be referred to as sensitivity-related information. Thecamera control unit 9 stores the acquired information in a volatilememory (not shown).

A control system power source 12 of the camera body 1 supplies power toeach of the imaging element 4, the photometric unit 5, the focusdetection unit 6, the image processing unit 8, the display unit 33, acontrol system circuit of the interchangeable lens 2, and the like. Inaddition, a driving system power source 13 of the camera body 1 suppliespower to the shutter control unit 7, a driving system circuit of theinterchangeable lens 2, and the like.

An imaging preparation switch SW1 14 and an imaging start switch SW2 15are control switches used when a user takes a photograph. The switch SW1is turned on by a half-push manipulation of a release button, and theswitch SW2 is turned on by a full-push manipulation of the releasebutton. In the AF control, corresponding processes are started by usinga signal of each of the switches SW1 and SW2 as a trigger.

The image recording unit 16 performs control for recording the acquiredimage data on a recording medium in a predetermined format. Amanipulation unit has various manipulation members and switches. In FIG.1, as a manipulation member according to the present embodiment, a focusdetection point change manipulation member 32 for selecting a focusdetection point is illustrated. The display unit 33 is configured todisplay captured images or various types of information of the camera.The various types of information include a display range for displayinga plurality of focus detection regions set on an image plane, and thelike.

An imaging optical system of the interchangeable lens 2 has a zoom lens21, a focus lens 22, an image blurring correction lens 23, and adiaphragm 24. The zoom lens 21 moves in an optical axis direction of theimaging optical system to change a focal length. The focus lens 22 is afocus adjustment lens moving in an optical axis direction of the imagingoptical system. The image blurring correction lens 23 corrects imageblurring caused by camera shake such as hand vibration by movingperpendicularly to the optical axis direction of the imaging opticalsystem. The diaphragm 24 is configured to change the amount ofphotographic light depending on an aperture size (f-number) throughvariable control of the aperture size.

An electric circuit module 20 has the lens communication unit 25, thelens control unit 26, and driving units. The driving units include azoom driving unit 27, a focus driving unit 28, a shake correctiondriving unit 29, and a diaphragm driving unit 30. The lens control unit26 receives the focus sensitivity information, the focus drivingcommand, and the like based on shooting information or a shooting statusof the camera body 1 through the camera communication unit 11 and thelens communication unit 25. The lens control unit 26 outputs a focusdriving signal to the focus driving unit 28 in response to the focusdriving command.

The focus driving unit 28 has an actuator such as a step motor, avibration motor, or a voice coil motor and moves the focus lens 22 to anin-focus position in response to the focus driving signal from the lenscontrol unit 26. That is, the AF processing of the interchangeable lens2 side is executed until the focus driving command is received, and thefocus lens 22 is moved to the in-focus position.

The lens control unit 26 outputs a diaphragm driving signal to thediaphragm driving unit 30 in response to the diaphragm driving commandacquired from the camera control unit 9. The diaphragm driving unit 30has an actuator such as a step motor and drives the diaphragm 24 inresponse to the diaphragm driving signal from the lens control unit 26.

When a user manipulates a zoom operation ring (not shown) provided inthe interchangeable lens 2, the lens control unit 26 outputs a zoomdriving signal to the zoom driving unit 27 in order to move the zoomlens 21 in the zoom direction at the zoom driving speed corresponding tothe manipulation. The zoom driving unit 27 has an actuator such as astep motor and drives the zoom lens 21 in response to the zoom drivingsignal from the lens control unit 26.

The lens control unit 26 outputs a shake correction driving signal tothe shake correction driving unit 29 in response to a shake detectionsignal from a shake detection sensor such as an angular velocity sensoror an acceleration sensor (not shown) provided in the interchangeablelens 2. The shake correction driving unit 29 has an actuator such as avoice coil motor and drives an image blurring correction lens 23 inresponse to the shake correction driving signal from the lens controlunit 26.

A memory unit 31 includes a storage device such as an electricallyerasable programmable read-only memory (EEPROM) or a flash ROM. Thememory unit 31 stores data including focus position deviationinformation, the focus sensitivity, and focus sensitivity image heightcorrection coefficient information used to correct a result of the focusdetection (defocus amount). In addition, the memory unit 31 may bedisposed inside the lens control unit 26. The lens control unit 26outputs the information read from the memory unit 31 to the lenscommunication unit 25, and the lens communication unit 25 transmits theinformation to the camera communication unit 11.

Next, an overview of the operation of the imaging apparatus will bedescribed. When a user manipulates the imaging preparation switch (SW1)14 to be ON, the camera control unit 9 causes the photometric unit 5 toperform a photometric operation and causes the focus detection unit 6 toperform a focus detection operation. According to the presentembodiment, a process of acquiring a sensitivity image height correctioncoefficient that varies depending on a distance (image height component)from the optical axis in addition to the sensitivity of the optical axis(image height of the center) acquired from the interchangeable lens 2 isperformed. The corrected sensitivity is acquired from the sensitivityimage height correction coefficient and the image height componentsubjected to the focus detection. For the defocus amount acquired as aresult of the focus detection, conversion to a driving amount (thenumber of pulses) to be instructed to the focus driving unit 28 isperformed using the corrected sensitivity information. The lens controlunit 26 performs focus driving control based on the driving amountinstructed by the camera control unit 9. As the focus detectionoperation and the lens driving operation are repeated, the defocusamount is gradually reduced. In this process, when the detected defocusamount is significant, the focus lens driving operation and focusdetection operation are overlappingly performed. That is, overlapdriving is performed. As described below, according to the presentembodiment, it is possible to reduce a communication load and acalculation load between the camera body 1 and the interchangeable lens2 even in the overlap driving.

When a user manipulates the imaging start switch (SW2) 15 to be ON, thecamera control unit 9 transmits a driving command of the diaphragm 24 tothe lens control unit 26, controls the f-number in photographing, andcauses the shutter control unit 7 to drive the shutter, so that theimaging element 4 is exposed at a predetermined shutter speed. Inaddition, the camera control unit 9 causes the image processing unit 8to create a recording image from the output of the imaging element 4.The imaging element 4 has focus detection pixels dedicated to theauto-focus operation. Therefore, it is possible to acquire the focusdetection signal along with the recording image. An auto-focus methodperformed by detecting phase differences using the imaging element 4 isalso called “image plane phase difference AF.” Alternatively, withoutbeing limited to the image plane phase difference AF, the focusdetection may be performed using an AF sensor dedicated to phasedifference detection. After the shooting, the camera control unit 9instructs the image recording unit 16 to record a recording image signalin a recording medium (not shown) such as a semiconductor memory. Thecaptured image is either a still image or a moving video. For example,if a still image shooting mode is selected using the mode selectionswitch, a still image is acquired. If a live-view mode or a moving videoshooting mode is selected, a moving video is acquired. In an imagingapparatus provided with a record start button for capturing a movingvideo, a moving video recording operation is started by manipulating therecord start button. A user is allowed to select a recording imagequality by manipulating a recording image quality setting switchprovided in the camera body 1.

Next, a configuration for focus detection processing according to thepresent embodiment will be described. A configuration of the imagingelement 4 will be described with reference to FIGS. 2A and 2B. FIG. 2Ais a schematic diagram illustrating the entire configuration of theimaging element 4. FIG. 2B is a schematic diagram illustrating a singlepixel of the imaging element 4. The imaging element 4 of FIG. 2A has apixel portion 201 consisting of a plurality of pixels arranged in a2-dimensional array shape. A vertical selection circuit 202 sequentiallyselects pixel signals from a plurality of rows of the pixel portion 201and outputs the selected signal to a read circuit 203. The read circuit203 reads the pixel signal selected by the vertical selection circuit202 out of the pixels of the pixel portion 201. The read circuit 203 hasa memory for accumulating signals, a gain amplifier, an analog/digitalconverter, and the like for each column. A horizontal selection circuit204 sequentially selects a plurality of pixel signals read by the readcircuit 203 for each column. A serial interface (SI/F) unit 205 acquiresinformation such as an operation mode of each circuit determined by anexternal device. Further, in addition to the elements of FIG. 2A, theimaging element 4 may have other elements such as a timing generatorconfigured to provide timing signals to the vertical selection circuit202, the horizontal selection circuit 204, the read circuit 203, and thelike, and a control circuit.

The pixel 206 of FIG. 2B has a single microlens 207 and a pair ofphotodiodes 208 and 209. A pair of photodiodes (PDs) serve as aphotoelectric converter for performing the image plane phase differenceAF. Further, the pixel 206 has a pixel amplifier for reading thephotodiode signal to the read circuit 203, a row selection switch, areset switch for resetting the photodiode signal, and the like inaddition to the elements of FIG. 2B.

FIG. 3 is a schematic diagram illustrating the pixel portion 201 of theimaging element 4. Since the pixel portion 201 provides a 2-dimensionalimage, a plurality of pixels are arranged in a 2-dimensional arrayshape. The pixels 301, 302, 303, and 304 have the configuration similarto that shown in FIG. 2B. The photodiodes 301L, 302L, 303L, and 304L aresimilar to the photodiode 208 shown in FIG. 2B. The photodiodes 301R,302R, 303R, and 304R are similar to the photodiode 209 shown in FIG. 2B.Although a bisected photoelectric converter is illustrated by way ofexample in the present embodiment, a segment direction and the number ofsegments may be changed arbitrarily depending on a requirement of theapparatus.

Detection of light on the imaging element 4 will be described withreference to FIG. 4. FIG. 4 is a conceptual diagram illustrating abundle of light beams that emerge from an exit pupil of the photographiclens and are incident on the imaging element. FIG. 4 schematicallyillustrates the image plane phase difference detection AF method. On apart of the cross section 401 of the imaging element 4, a microlens 402(corresponding to the microlens 207 of FIG. 2B) and a color filter 403are illustrated. The photodiodes 404 and 405 correspond to thephotodiodes 208 and 209 of FIG. 2B.

A center of the bundle of light beams that emerge from the exit pupil406 of the photographic lens with respect to the pixel provided with themicrolens 402 is indicated by the optical axis 409. The bundle of lightbeams that emerge from the exit pupil 406 is incident on the imagingelement 4 and the bundle of light beams is centered on the optical axis409. Pupil regions 407 and 408 are a part of the area of the exit pupil406 of the photographic lens. The light beams 410 and 411 are lightbeams located on the outermost circumference of the bundle of lightbeams passing through the pupil region 407. The light beams 412 and 413are light beams located on the outermost circumference of the bundle oflight beams passing through the pupil region 408. Out of the bundle oflight beams that emerge from the exit pupil 406, the upper part of thebundle of light beams is incident on the photodiode 405, and the lowerpart of the bundle of light beams is incident on the photodiode 404 withrespect to the optical axis 409. That is, the photodiodes 404 and 405receive the bundle of light beams passing through different regions onthe exit pupil 406 of the photographic lens.

Although a pair of photodiodes are provided for a single microlens inFIGS. 2B and 3, the invention is not limited thereto. For example, aphotodiode of one side may be used for a certain pixel, and a photodiodeof the opposite side may be used for neighboring pixels. That is, theimage plane phase difference AF can be achieved as long as the opticalimages passing through different regions of the exit pupil 406 of thephotographic lens are acquired on the image plane of the imagingelement.

The imaging element 4 is arranged in a 2-dimensional array shapeincluding A-line pixels and B-line pixels that receive a bundle of lightbeams from different pupil regions of the photographic lens.Specifically, in FIG. 3, out of the pixels 301, 302, 303, and 304 of therow 305, pixels of the photodiodes 301L, 302L, 303L, and 304L areincluded in the A-line pixels. In addition, the pixels of thephotodiodes 301R, 302R, 303R, and 304R are included in B-line pixels.For each output of the A-line and B-line pixels, an interval between twoimages (image spacing) is different depending on whether the image hasan in-focus state, a front defocus state, or a rear defocus state. Adefocus amount corresponding to the image spacing is calculated, andfocus adjustment is performed by moving the focus lens 22 into thein-focus state. That is, the movement amount of the focus lens 22 can becalculated based on an image deviation amount between two images.Although the description has been made for two images (including animage of the A-line pixels and an image of the B-line pixels) andneighboring pixel lines for simplicity purposes in the presentembodiment, the A-line pixels and the B-line pixels are classified basedon the color filter in practice.

In the focus detection process, the image formed by the bundle of lightbeams passing through pupil regions having different optical systems isphotoelectrically converted to generate a pair of image signals. Thefocus detection unit 6 detects a defocus amount based on a phasedifference (image deviation amount) between the pair of image signals. Afocus driving amount is calculated based on the detected defocus amount,and the driving of the focus lens is controlled based on the focusdriving amount.

Next, a multi-point AF control method for focus detection across a widerange of the image height will be described as the image plane phasedifference AF control according to the present embodiment with referenceto FIG. 5. FIG. 5 is an explanatory diagram illustrating a multi-pointfocus detection frame based on a phase difference detection method. Apixel area 500 in the image plane is an area of pixels inside theimaging element 4 in which pixels dedicated to the phase differencedetection method are arranged. The pixel area 500 indicates a shootingrange. Since the pixel 501 dedicated to the phase difference detectionmethod is arranged in the horizontal and vertical directions, a phasedifference image signal for a subject can be acquired from eachdirection. A rectangular region acquired by combining a plurality oflines passing through the dedicated pixel 501 is defined as an AF frameregion 502. The AF frame region 503 is a region including a single groupsurrounded by the dotted rectangular frame. In the coordinate system 504of FIG. 5, “X” denotes a horizontal axis, and “Y” denotes a verticalaxis.

When focus detection is performed using an AF frame arbitrarily selectedby a user, the focus detection process is performed for the selected AFframe region 502. Meanwhile, in the case of subject tracking such asface recognition or multi-point auto-focus, the focus detection processis performed for all AF frames including the entire shooting range. Inthe example of FIG. 5, the focus detection process is performed for atotal of 36 AF frames acquired by dividing the shooting rangehorizontally and vertically into “6×6.” In FIG. 5, the numerals “1” to“36” are allocated from the upper left to the lower right to identifyeach AF frame.

However, as the number of pixels, the number of the multi-point AFframes, or a frame rate increases, it may be difficult to perform thefocus detection process within a single vertical period 1V. In thiscase, it is difficult to perform focus detection across the entireshooting range at one time. In this regard, the shooting range isdivided into a plurality of ranges, and the focus detection process isexecuted sequentially for the plurality of ranges. Specifically, asillustrated in FIG. 6, the focus detection process is executed for eachof the focus detection regions acquired by dividing the shooting range.In FIG. 6, the shooting range is divided into nine groups of fourregions, and the focus detection is performed for each group. In thiscase, in the focus detection process, what AF frame is employed is notyet determined. For this reason, the camera control unit 9 acquiresfocus-sensitivity-related information from the lens control unit 26. Inthe correction process using the focus-sensitivity-related information,image height position information of each AF frame is necessary.Therefore, 2-dimensional coordinate information is acquired by settingthe coordinate system 504 of FIG. 5. A position is represented bycoordinates (X, Y) on the X-Y plane by setting the image height of thecenter of the coordinate system 504 to zero.

The region 510 of FIG. 6 (including AF frames 1, 2, 7, and 8)corresponds to the pixel 501 dedicated to the phase difference detectionmethod of FIG. 5. A rectangular frame 511 surrounded by the dotted lineindicates a region in which the focus detection process can be performedby grouping a plurality of AF frames at one time. The entire shootingrange is covered by the rectangular frames 511 to 519, and a focusdetection region is acquired by grouping four frames to a single set, sothat the focus detection process is executed repeatedly using eachoutput of nine frames. Specifically, during three initial verticalperiods 1V to 3V, the focus detection region is shifted sequentially forthe rectangular frames 511, 512, and 513, and focus detection isperformed for an upper part of the imaging element 4. During the nextthree vertical periods 4V to 6V, the focus detection region is shiftedsequentially for the rectangular frames 514, 515, and 516, so that thefocus detection is performed for a center part of the imaging element 4.Furthermore, during the next three vertical periods 7V to 9V, the focusdetection region is shifted sequentially for the rectangular frames 517,518, and 519, so that the focus detection is performed for a lower partof the imaging element 4. In this manner, during the vertical periods 1Vto 9V, the focus detection signals are acquired across the entireshooting range.

Next, focus detection timings for the multi-point AF frames will bedescribed with reference to FIG. 7. FIG. 7 is a timing chart acquired byrepeatedly performing the focus detection using nine frames of FIG. 6.The signal 601 indicates a behavior of a signal line used inphotographing in a time-series manner. A start timing of the imagingprocess is indicated by a time point of the falling edge of the signal601 in a period corresponding to the frame rate, that is, the VD signalperiod. The trapezoid 602 indicates an accumulation timing of theimaging element 4. The accumulation control of the imaging element 4 isperformed within the VD signal period, and the accumulation in an upperpart of the imaging element is performed in the vicinity of the leadingedge of the VD signal. As reading in the lower part of the imagingelement is performed, the accumulation is performed at a latter half ofthe VD signal period. According to the present embodiment, since thepixel dedicated to phase difference detection is arranged in the imagingelement 4, the accumulation timing of the AF pixel is determined by aposition of the AF frame. Processing for the nine frames of FIG. 6 willnow be described with reference to the timing chart of FIG. 7.

In the initial three vertical periods 1V to 3V, the AF pixels in theupper part of the imaging element 4 are used. Therefore, the phasedifference detection signal is acquired at the timing 610 for “UPPERBLOCK AF ACCUMULATION.” In the next three vertical periods 4V to 6V, theAF pixels in the center part of the imaging element 4 are used.Therefore, the phase difference detection signal is acquired at thetiming 611 for “CENTER BLOCK AF ACCUMULATION.” Further, in the nextthree vertical periods 7V to 9V, the AF pixels in the lower part of theimaging element are used. Therefore, the phase difference detectionsignal is acquired at the timing 612 for “LOWER BLOCK AF ACCUMULATION.”

Meanwhile, the camera control unit 9 acquires thefocus-sensitivity-related information from the lens control unit 26 atthe timings 620 to 628 corresponding to “ACQUIRE SENSITIVITY-RELATEDINFORMATION (1) to (9),” that is, at each falling edge of the signal601. The camera control unit 9 stores timing information correspondingto each frame 1V to 9V in the memory in association with the acquiredfocus-sensitivity-related information. The defocus status of all AFframes is determined by acquiring a result of the focus detection forthe nine frames. Therefore, selection of the AF frame is allowed at theselection timing 629 indicated by “AF FRAME SELECTION PROCESS.” As acriterion for selecting the AF frame, for example, the closest AF rangemay be selected, or a waveform of the phase difference detection resultof the focus detection having highest reliability may be selected, asnecessary. In addition, so-called overlap control in which the focuslens is driven in the course of focus detection may also be performed.In this case, it is necessary to consider the lens driving amount fromthe timing at which the focus detection process starts to the timing atwhich the AF frame is determined as an idle running amount. In order toacquire the lens idle running amount, data of each timing t1 to t9 isstored in the memory at the timings 630 to 638 indicated by “STORETIMINGS (1) to (9)” corresponding to the falling edges of the VD signalfor each of the nine frames. In addition, at the AF frame selectiontiming 639, the timing t_sel at that time point is acquired. In theprocess of calculating the lens idle running amount, when therectangular frame 512 of FIG. 6 set as, for example, a second verticalperiod 2V is selected, it is conceived that the focus lens is driven ata constant speed for a period from the timing t2 to the timing t_sel.The movement amount of the focus lens that moves at a constant speed iscalculated as the lens idle running amount. The focus detection resultacquired at the second vertical period 2V is converted into the focusdriving amount using the accurate sensitivity acquired from Formula (1)below, and the lens idle running amount is subtracted therefrom, so thatit is possible to acquire the lens driving amount necessary for thein-focus state.

Next, a multi-point auto-focus process performed by the camera controlunit 9 according to the present embodiment will be described withreference to the flowchart of FIG. 8. In step S701, a user sets a focusdetection point automatic selection mode using a focus detection pointchange manipulation member 32 included in a manipulation unit of thecamera. When the imaging preparation switch (SW1) 14 is turned on, thecamera control unit 9 starts the multi-point auto-focus process.

In step S702, in order to set the blocks indicated by the rectangularframe 511 in FIG. 6 as the AF frame, the camera control unit 9 setscontrol information in the focus detection unit 6. In step S703, thecamera control unit 9 detects the VD signal of the photographing anddetermines whether or not there is a VD interruption. The VDinterruption is generated periodically depending on the VD signal. Instep S703, if the VD signal is detected, the process advances to stepS704. If the VD signal is not detected, the determination process ofstep S703 is repeated.

In step S704, the camera control unit 9 acquires thefocus-sensitivity-related information from the lens control unit 26through the lens communication unit 25 and the camera communication unit11. The “sensitivity information at the image height of the center” ofthe focus-sensitivity-related information is information determinedbased on the optical information stored in the lens control unit 26. Theoptical information includes information on positions of the zoom lens21, the focus lens 22, and the image blurring correction lens 23, thef-number of the diaphragm 24, information on accessories (such as anextender) (not shown), and the like. The sensitivity information isinformation indicating a value at the center of the image plane, thatis, a value at the zero image height (the image height of the center).In addition, the “sensitivity image height correction coefficient” ofthe focus-sensitivity-related information is a focus sensitivitycorrection coefficient for correcting the focus sensitivity indicated bythe “sensitivity information at the image height of the center” acquiredfrom the lens control unit 26. The origin on the X-Y plane of FIG. 5,that is, the coordinates of the image height of the center, is denotedby “(0, 0).” The sensitivity S(X, Y) of the image height coordinates (X,Y) can be calculated using an X-Y polynomial as expressed in thefollowing Formula (1).[Formula 1]S(X,Y)=S ₀×(a ₀ +a ₁ X ² +a ₂ X ⁴ +a ₃ Y ² +a ₄ Y ⁴ +a ₅ X ² Y ²)  (1)

In Formula (1), “S0” denotes focus sensitivity acquired from the lenscontrol unit 26. Each of factors “a0” to “a5” denotes a focussensitivity correction coefficient. In this manner, a coefficientindicating a change amount of the sensitivity depending on the imageheight is included in the data acquired by the camera control unit 9from the lens control unit 26. The sensitivity information according tothe present embodiment is information calculated through polynomialapproximation for a characteristic of the focus sensitivity for theimage height of the center. Alternatively, the sensitivity informationaccording to the present embodiment may be calculated through linearapproximation.

In addition to the method described above, the camera control unit 9 maygive the image height information to the lens control unit 26, and thesensitivity information of the image height instructed to the lenscontrol unit 26 may be transmitted to the camera control unit 9.However, since this method relates to an increase of the multi-points ofthe AF frame or an increase of the frame rate, a communication bandbetween the camera control unit 9 and the lens control unit 26 maybecome short, or the calculation load of the control unit may increase.Therefore, it is preferable that the camera control unit 9 acquire thefocus sensitivity correction coefficient from the lens control unit 26as in the present embodiment in terms of the load reduction.

In step S705, it is determined whether or not the accumulation ofAF-dedicated pixels in the imaging element 4 is completed. If it isdetermined that the accumulation of AF-dedicated pixels is completed,the camera control unit 9 advances the process to step S706. If it isdetermined that the accumulation of AF-dedicated pixels is notcompleted, the camera control unit 9 waits for the completion. In stepS706, the AF-dedicated pixels corresponding to the AF frame position setin step S702 are read, and the focus detection unit 6 acquires the focusdetection information of the phase difference detection. In step S707,the camera control unit 9 stores the focus detection informationacquired in step S706 and the sensitivity-related information acquiredin step S704 in the memory in association with each other.

In step S710, it is determined whether or not the focus detection forthe AF-dedicated pixels of all AF frames has been completed. The cameracontrol unit 9 determines whether or not the focus detection isrepeatedly performed for the area indicated by the rectangular frames511 to 519 of FIG. 6. If it is determined that the focus detection isnot completed for all of the AF frames, the camera control unit 9returns the process to step S702 and continues the process by resettingthe next focus detection region to the AF frame position. If it isdetermined that the focus detection is completed for all of the AFframes, the process advances to step S711.

In step S711, an AF frame position selection process is performed. Anoptimum focus detection result is selected from the focus detectionresults for all of the AF frames, specifically, the focus detectionresults for nine frames across the area of the rectangular frames 511 to519 of FIG. 6. The optimum focus detection result is determined by thecamera control unit 9 from the focus detection signals satisfying the AFframe selection criterion based on a predetermined determinationcriterion. In step S712, the camera control unit 9 acquires thefocus-sensitivity-related information associated with the focusdetection result stored in step S707 for the focus detection resultselected in step S711. That is, the focus-sensitivity-relatedinformation for the focus detection result selected in step S711 isacquired based on a relationship between the acquired focus detectioninformation and the focus-sensitivity-related information. In this case,an additional process such as interpolation is executed as necessary.

In step S713, the camera control unit 9 executes a calculation processby applying Formula (1) to the image height position of the AF frameselected in step S711 using the focus-sensitivity-related informationacquired in step S712. As a result, focus sensitivity informationcorrected with high accuracy is calculated. In step S714, the focus lensdriving amount is calculated from the focus detection result using thefocus sensitivity information calculated in step S713. That is, thecamera control unit 9 calculates a pulse count for driving the focuslens 22 from the defocus amount as the focus detection result. Thecamera control unit 9 transmits a driving instruction including thecalculated pulse count to the lens control unit 26 to request focusdriving. In step S715, the AF frame position selection process under themulti-point AF control is completed.

According to the present embodiment, for example, when the focusdetection results are acquired at a plurality of VD signal timings, theprevious focus detection result, that is, the history data, is read fromthe memory for use. In this case, a process of storing the focusdetection results and the focus-sensitivity-related information inassociation with each other is performed. The camera body acquires acorrection coefficient for correcting the sensitivity in considerationof the image height along with the sensitivity information of the imageheight of the center, determines the AF frame position, and calculatesthe focus sensitivity information. In focusing at the surrounding imageheight, it is possible to correct the focus sensitivity change amountdepending on the position of the focus detection using an optimum AFcontrol method. According to the present embodiment, even when thenumber of multi-point auto-focus frames and the frame rate increase, itis possible to apply optimum sensitivity information while reducing thecalculation load. Therefore, it is possible to provide aninterchangeable camera-lens system capable of improving focus adjustmentaccuracy.

In the present embodiment, the multi-point auto-focus mode has beendescribed as a control mode for dividing the area of the image plane ina grid shape and executing the focus detection for each divided focusdetection region. Alternatively, the aforementioned process may beapplied to a zonal AF mode in which the focus detection is executed foreach predetermined zone. This similarly applies to other embodimentsdescribed below.

Second Embodiment

Next, a second embodiment of the invention will be described. Accordingto the present embodiment, the camera control unit 9 has a driving rangefor determining the focus detection result (defocus amount) used in thefinal driving of the focus lens 22 when the camera control unit 9performs the phase detection AF control. This driving range correspondsto a length acquired by multiplying a permissible circle of confusion ofthe imaging element 4 by an arbitrary ratio, and will be referred to asa “final driving range.” The camera control unit 9 selects a sensitivitycorrection execution range from the final driving range and determineswhether or not the focus detection result (defocus amount) is within thesensitivity correction execution range. If it is determined that thefocus detection result is within the sensitivity correction executionrange, the corresponding focus detection result is used in the finaldriving. As a result, it is possible to realize an in-focus operationthrough AF control without generating a hunting phenomenon. Note that,in the present embodiment, like reference numerals denote like elementsas in the first embodiment, and the description will focus ondifferences without repeatedly describing such elements.

Multi-point auto-focus processing in the camera body side according tothe present embodiment will be described with reference to the flowchartof FIG. 9. In step S801, an AF frame position selection process isinitiated, so that the process of steps S802 and S803 is executed. Theprocess of steps S802 and S803 is similar to the process of steps S702and S703 of FIG. 8, and will not be repeatedly described.

Then, in step S804, the camera control unit 9 acquires thefocus-sensitivity-related information from the lens control unit 26through the lens communication unit 25 and the camera communication unit11. Out of the focus-sensitivity-related information, the sensitivityindicated by the “sensitivity information at the image height of thecenter” refers to a value at the center of the image plane, that is, avalue at the zero image height (image height of the center). The processof steps S805, S806, S807, and S810 is similar to the process of stepsS705, S706, S707, and S710 of FIG. 8. However, in step S807, the focusdetection information acquired in step S806 and the sensitivity-relatedinformation acquired in step S804 (sensitivity information at the zeroimage height) are stored in the memory in association with each other.

In step S810, when the focus detection is completed for all of the AFframes, the process advances to step S811. In step S811, the cameracontrol unit 9 sets the sensitivity correction execution range. First,the camera control unit 9 acquires focal length information of theimaging optical system through the lens communication unit 25 and thecamera communication unit 11. Then, the camera control unit 9 calculatesthe sensitivity correction execution range from the overall focusdetection results, specifically, from the focus detection result fromthe nine frames repeatedly performed for the area indicated by therectangular frames 511 to 519 of FIG. 6 based on image heightinformation of the AF frame farthest from the image height of thecenter. The calculation method will be described below with reference toFIG. 10.

The process of steps S812 and S813 is similar to the process of stepsS711 and S712 of FIG. 8. However, in step S813, for the focus detectionresult selected in step S812, the focus-sensitivity-related informationassociated with the focus detection result stored in step S807(sensitivity information at the zero image height) is acquired.

In step S814, the camera control unit 9 determines whether or not thesensitivity correction process is performed based on the sensitivitycorrection execution range set in step S811 and the focal lengthinformation acquired in step S811. The defocus amount is calculatedbased on the focus detection result at the AF frame position selected instep S812 and the focus-sensitivity-related information acquired in stepS813. The camera control unit 9 determines that the sensitivitycorrection process is performed if the calculated defocus amount iswithin the sensitivity correction execution range set in step S811. Ifthe defocus amount is not within the sensitivity correction executionrange set in step S811, it is determined that the sensitivity correctionprocess is not performed. The determination process will be describedbelow in more detail with reference to FIG. 11. In addition, the cameracontrol unit 9 determines that the sensitivity correction process is notperformed if the focal length is longer than a predetermined thresholdvalue. If it is determined that the sensitivity correction process isperformed, the process advances to step S815. If it is determined thatthe sensitivity correction process is not performed, the processadvances to step S817. Note that the criterion for determining whetheror not the sensitivity correction process is performed may be selectedfrom those other than that of the present embodiment as necessary.

In step S815, the camera control unit 9 acquires data on the“sensitivity image height correction coefficient” from the lens controlunit 26 through the lens communication unit 25 and the cameracommunication unit 11. This data is data on the focus sensitivitycorrection coefficient for correcting the focus sensitivity of the imageheight of the center. The sensitivity S(X, Y) is calculated based onFormula (1) described above. The process of step S816 and S817 issimilar to the process of steps S713 and S714 of FIG. 8. In step S818,the AF frame position selection process for the multi-point auto-focusprocessing is terminated.

Next, a sensitivity correction execution range calculation method willbe described with reference to FIG. 10. In FIG. 10, the ordinate denotesthe image height (in units of millimeters), and the abscissa denotes aratio. In addition, the sensitivity ratio and the sensitivity correctionratio are illustrated at the focal lengths A and B (in units ofmillimeters). The camera control unit 9 calculates the sensitivitycorrection ratio from the image height and a coefficient (referred to as“α”) that varies depending on the stored focal length. The image heightis acquired from the image height coordinates (X, Y) of the AF framefarthest from the image height of the center set in step S811 of FIG. 9using Formula (2) below. The sensitivity correction ratio is acquired byapplying the image height and the coefficient α to Formula (3) below.image height=√(X ² +Y ²)  (2)sensitivity correction ratio=1+(image height×α)  (3)

In FIG. 10, a curve 901 indicated by the solid line represents asensitivity ratio at the focal length of A mm, and a curve 902 indicatedby the solid line represents a sensitivity ratio at the focal length ofB mm. Both the sensitivity ratios are set to “1” at the zero imageheight and increase as the image height increases. If the sensitivityratio at the focal length of A mm has a characteristic represented onthe curve 901, the sensitivity correction ratio calculated from Formulas(2) and (3) is represented on the curve 903 indicated by the one-dottedchain line. The value of the sensitivity correction ratio is set to “1”at the zero image height and linearly increases as the image heightincreases. In addition, if the sensitivity ratio at the focal length ofB mm has a characteristic indicated by the curve 902, the sensitivitycorrection ratio calculated from Formulas (2) and (3) is represented onthe curve 904 indicated by the one-dotted chain line. The value of thesensitivity correction ratio is set to “1” at the zero image height andlinearly increases as the image height increases. The inclinationthereof is larger than that of the curve 903.

The camera control unit 9 calculates the sensitivity correctionexecution range by applying the calculated sensitivity correction ratioand the final driving range to Formula (4) below.sensitivity correction execution range=sensitivity correctionratio×final driving range  (4)

According to the present embodiment, calculation of the sensitivitycorrection ratio is expressed as a primary interpolation function of theimage height, and calculation of the sensitivity correction executionrange is expressed as a primary function of the sensitivity correctionratio. However, such expressions are only for exemplary purposes, andany other interpolation functions and expressions may also be employed.In addition, the camera control unit 9 may acquire data on thecoefficient α from the lens control unit 26 through the lenscommunication unit 25 and the camera communication unit 11.

A method of setting the sensitivity correction execution range and amethod of determining whether or not the sensitivity correction processis performed will be described with reference to FIG. 11. FIG. 11 is anexplanatory diagram illustrating a relationship between the defocusamount, the final driving range 1001, the sensitivity correctionexecution range 1002, and the sensitivity correction non-execution range1003. The sensitivity correction execution range 1002 is calculated instep S811 of FIG. 9 using Formula (4), and the final driving range 1001is set as a center. The final driving range 1001 is a predeterminedrange centered at the zero position of the defocus amount, and a rangeacquired by multiplying the sensitivity correction ratio by the finaldriving range 1001 is set to the sensitivity correction execution range1002. The camera control unit 9 determines whether the defocus amountcalculated based on the focus detection result selected in step S812 andthe focus-sensitivity-related information acquired in step S813 iswithin the sensitivity correction execution range 1002 or thesensitivity correction non-execution range 1003. If the defocus amountis within the sensitivity correction execution range 1002, it isdetermined in step S814 of FIG. 9 that the sensitivity correctionprocess is executed. If the defocus amount is within the sensitivitycorrection non-execution range 1003, it is determined in step S814 thatthe sensitivity correction process is not executed.

According to the present embodiment, the focus sensitivity correctionprocess is executed only within the sensitivity correction executionrange set in the vicinity of the final driving range and acquired byreflecting a change of the focus sensitivity depending on the imageheight. According to the present embodiment, it is possible to improvefocus adjustment accuracy while a communication load between the camerabody and the lens unit and the calculation load of the camera body arereduced. Furthermore, the embodiments of the invention can beeffectively applied to an increase of the number of frames in themulti-point auto-focus operation and an increase of the frame rate.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the present inventionis not limited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2015-161604, filed Aug. 19, 2015 which is hereby incorporated byreference wherein in its entirety.

What is claimed is:
 1. A lens apparatus t is capable of being mounted toa camera apparatus, the lens apparatus comprising; an imaging opticalsystem including a lens; and at least one processor executing computerexecutable instructions or at least one circuit which functions as; acommunication unit configured to communicate with a camera apparatus;and a control unit configured to control communication of thecommunication unit and driving of the lens; wherein the control unittransmits, through the communication unit, a first information for conyling a focus detection signal to a driving amount of the lens and asecond information corresponding to a change of the first informationaccording to an image height, wherein the control unit controls drivingof the lens based on a control signal indicating the driving amount ofthe lens received by the communication unit, and wherein the controlunit transmits the second information through the communication unitcorresponding to every focus detection und a control mode in which thefocus detection is performed for focus detection regions at differenttimings.
 2. The lens apparatus according to claim 1, wherein the secondinformation include plurality of information each corresponding to oneof the focus detection regions, each of the focus detection correspondsto different image height.
 3. The lens apparatus according to claim 1,wherein the control signal indicates the driving signal generated basedon the first information and the second information corresponding to theimage height of the selected focus detection region.
 4. A control methodof a lens apparatus that is capable of being mounted to a cameraapparatus and comprises an imaging optical system including a lens, themethod comprising: communicating with a camera apparatus, controllingcommunication of driving of the lens; transmitting a first informationfor converting a focus detection signal to a driving amount of the lensand a second information corresponding to a change of the firstinformation according to an image height; controlling driving of thelens based on a control signal indicating the driving amount of thelens; and transmitting the second information in every focus detectiontiming under a control mode in which the focus detection is performedfor focus detection regions at different timings.
 5. An imagingapparatus comprising: at least one processor executing computerexecutable instructions or at least one circuit which functions as: acommunication unit configured to communicate with a unit provided with afocus adjustment lens; a detection unit configured to acquire a focusdetection signal in a plurality of regions; and a control unitconfigured to generate a control signal for controlling driving of thelens based on the focus detection signal and transmit the control signalto the lens unit through the communication unit, wherein the controlunit acquires, through the communication unit from the lens unit, afirst information for converting a focus detection signal to a drivingamount of the lens and a second information corresponding to a change ofthe first information according to an image height, wherein the controlunit selects a region used to control the driving of the lens from theplurality of the regions after acquiring the first information and thesecond information, wherein the control unit generates the drivingamount of the lens as the control signal from the first information andthe second information depending on the image height of the selectedregion, and wherein the control unit acquires at least the firstinformation from the lens unit in every focus detection timing under acontrol mode in which the focus detection is performed for the pluralityof the plurality of regions at different timings.
 6. The imagingapparatus according to claim 5, wherein the control unit classifies theplurality of the regions into a plurality of groups and repeatsacquiring the of the second information in units of the groups.
 7. Theimaging apparatus according to claim 6, wherein a position of the lensmoves while repeating the acquiring of the second information.
 8. Theimaging apparatus according to claim 5, wherein the detection unitacquires the focus detection signal in a plurality of focus detectionregions set within an image plane.
 9. The imaging apparatus according toclaim 5, wherein the control unit calculates the driving amount of thelens using an information based on the first information and the secondinformation, if a defocus amount indicated by the focus detection signalis within a predetermined execution range.
 10. The imaging apparatusaccording to claim 9, wherein the control unit sets the execution rangeusing a correction ratio calculated from the image height.
 11. Theimaging apparatus according to claim 5, wherein the control unit storesthe focus detection signals acquired at different timings, theconversion information, and the correction information in a memory unitin association with each other, and acquires at least the secondinformation corresponding to the focus detection region selected fromthe plurality of the focus detection regions from the memory unit. 12.The imaging apparatus according to claim 6, wherein the group isobtained by dividing the area of the image plane in a grid shape, andthe control unit executes the focus detection for each of the dividedfocus detection regions.
 13. A control method of an imaging apparatus,the method comprising: communicating with a lens unit provided with afocus adjustment lens; acquiring a focus detection signal in a pluralityof regions; generating a control signal for controlling driving of thelens based on the focus detection signal and transmit the control signalto the lens unit; acquiring, from the lens unit, a first information forconverting a focus detection signal to a driving amount of the lens anda second information corresponding to a change of the first informationaccording to an image height; selecting a region used to control thedriving of the lens from the plurality of the regions after acquiringthe first information and the second information; generating the drivingamount of the lens as the control signal from the first information andthe second information depending on the image height of the selectedregion, and acquiring at least the first information from the lens unitin every focus detection timing under a control mode in which the focusdetection is performed for the plurality of regions at different timing.